Organic dyes containing coplanar dihexyl-substituted dithienosilole groups for efficient dye-sensitised solar cells

peer-reviewedA chromophore containing a coplanar dihexyl-substituted dithienosilole (CL1) synthesised for use in dye-sensitised solar cells displayed an energy conversion efficiency of 6.90% under AM 1.5 sunlight irradiation. The new sensitiser showed a similar fill factor and open-circuit voltage when compared with N719. Impedance measurements showed that, in the dark, the charge-transfer resistance of a cell using CL1 in the intermediate-frequency region was higher compared to N719 (69.8 versus 41.3 Omega). Under illumination at AM 1.5G-simulated conditions, the charge-transfer resistances were comparable, indicative of similar recombination rates by the oxidised form of the redox couple. The dye showed instability in ethanol solution, but excellent stability when attached to TiO2. Classical molecular dynamics indicated that interactions between ethanol and the dye are likely to reduce the stability of CL1 in solution form. Time-dependent density functional theory studies were performed to ascertain the absorption spectrum of the dye and assess the contribution of various transitions to optical excitation, which showed good agreement with experimental results.PUBLISHEDpeer-reviewe

Study of translational, librational and intra-molecular motion of adsorbed liquid water monolayers at various TiO2 interfaces

Equilibrium classical molecular dynamics (MD) simulations have been performed to investigate the vibrational motion of water in contact with rutile-(110), rutile-(100), rutile-(001), anatase-(101) and anatase-(001) surfaces at room temperature (300 K). The vibrational density of states (VDOS) of the first adsorbed monolayer of liquid water has been analysed for each surface. These have been compared with reported experimental INS values involving rutile and anatase polymorph surfaces, along with ab initio MD results. It is observed that good qualitative agreement is obtained for the rutile-(110) and the anatase-(101) surfaces with the corresponding experimental VDOS. A significant contribution from librational dynamics is found for planar rutile surfaces, but no such demarcation is seen in the experimental VDOS.Science Foundation IrelandIrish Research Council for Science, Engineering and TechnologyOther funderIrish Centre for High-End Computing18M embargo - release after 19/04/2013 - AV 15/11/2011; ke, vo, is, st, en - TS 15.11.1

Electrophoretic deposition of poly(3-decylthiophene) onto gold-mounted cadmium selenide nanorods

Molecular mechanisms of electrophoretic deposition (EPD) of P3DT poly(3-decylthiophene) molecules onto vertically aligned cadmium selenide arrays have been studied using large-scale, nonequilibrium molecular dynamics (MD), in the absence and presence of static external electric fields. The field application and larger polymer charges accelerated EPD. Placement of multiple polymers at the same lateral displacement from the surface reduced average deposition times due to ‘crowding’, giving monolayer coverage. These findings were used to develop and validate Brownian dynamics simulations of multi-layer polymer EPD in scaled-up systems with larger inter-rod spacings, presenting a generalised picture in qualitative agreement with random sequential adsorption

The influence of Ti and Si doping on the structure, morphology and photo-response properties of α-Fe2O3 for efficient water splitting: experiment and first-principle calculations

Ti- and Si- doping effects on morphology, structure, optical and photo-response of α-Fe2O3 nanoscale coatings from atmospheric-pressure chemical vapour deposition (APCVD) have been studied. Si- and Ti-doping led to larger clusters with finer grains and smaller clusters with larger grains, respectively. Photocurrent performance was increased remarkably by doping, especially Si. Excellent agreement was found for band gaps and optical properties compared to hybrid-Density Functional Theory. Substitutional replacement of Fe by Si shrinks the volume more than Ti-doping; it is conjectured that this affects hopping probability of localised charge-carriers more and leads to enhanced photocurrent activity for Si-doping, supported by experiment.Science Foundation IrelandAuthor has checked copyrightAD 09/01/201

Molecular dynamics study of water in contact with TiO2 rutile-110, 100, 101, 001 and anatase-101, 001 surface

We have carried out classical molecular dynamics of various surfaces of TiO2 with its interface with water. We report the geometrical features of the first and second monolayers of water using a Matsui Akaogi (MA) force field for the TiO2 surface and a flexible single point charge model for the water molecules. We show that the MA force field can be applied to surfaces other than Rutile-(110). It was found that water OH bond lengths, H-O-H bond angles and dipole moments do not vary due to the nature of the surface. However, their orientation within the first and second monolayers suggest that planar Rutile-(001) and Anatase-(001) surfaces may play an important role in not hindering removal of the products formed on these surfaces. Also, we discuss the effect of surface termination in order to explain the layering of water molecules throughout the simulation box.Science Foundation IrelandIrish Research Council for Science, Engineering and TechnologyOther funderIrish Centre for High End Computing12M embargo: release in May 2012 - AV 24/05/2011Duplicate item withdrawn - OR 17/08/201

Hydrogen bond dynamical properties of adsorbed liquid water monolayers with various TiO2 interfaces

Equilibrium classical molecular dynamics (MD) simulations have been performed to investigate the hydrogen bonding kinetics of water in contact with rutile-(110), rutile-(101), rutile-(100), and anatase-(101) surfaces at room temperature (300 K). It was observed that anatase-(101) exhibits the longest-lived hydrogen bonds in terms of overall persistence, followed closely by rutile-(110). The relaxation times, defined as the integral of the autocorrelation of the hydrogen bond persistence function, were also larger for these two cases, while decay of autocorrelation function was slower. The increased number and overall persistence of hydrogen bonds in the adsorbed water monolayers at these surfaces, particularly for anatase-(101), may serve to promote possible water photolysis activity thereon.Science Foundation IrelandOther funderIrish Centre for High End ComputingEmbargo 12 month

Analysis of gas adsorption in Kureha active carbon based on the slit-pore model and Monte-Carlo simulations

We analyse the adsorption of carbon dioxide and several light alkenes and alkanes on Kureha active carbon at a range of temperatures. We find generally good agreement between the alkene and alkane isotherms at moderate to high pressure, but find that at the lowest relative pressures for each gas there are significant discrepancies that seem to be correlated with the strength of gas-surface interactions. This pattern is similar to that observed in our previous work on the adsorption of light alkenes and alkanes on active carbon, except the errors here are much smaller. One possible explanation for this error is poor diffusion in the experiments at the lowest relative pressures, leading to measurements of non-equilibrium states. We suggest that this poor diffusion might be caused by potential barriers (i.e. it is activated diffusion) in the narrowest pores. We also find that our analysis of the adsorption of carbon dioxide at 273 K is inconsistent with all the alkene and alkane data. We suggest this discrepancy arises because our model of gas-surface interactions does not take contributions from polar surface sites into account. Although this study is specific to Kureha active carbon, we expect that our conclusions are relevant to other studies of gas adsorption on active carbon; they highlight the need for great care when taking measurements at low pressures, and motivate improvements in molecular models for gas adsorption in active carbons